1. Field of the Invention
The present invention relates generally to a TV lens system, and more particularly to a TV lens system having an analog control mode with an analog control system and a digital control mode using a serial communication function in order to transmit signals between a lens apparatus, a lens drive apparatus and a control unit for controlling them.
2. Description of Related Art
A television (TV) lens apparatus for a TV camera has a serial communication function for transmitting and receiving plural pieces of information on one line in a digital serial communication or a analog communication function for transmitting and receiving plural pieces of information with low level signals and high level signals or analog voltage signals (hereinafter referred to as analog signals) on a plurality of lines according to types of information. In view of this, there have already been proposed an automatic determination apparatus for detecting the presence of the serial communication to enable the TV lens system to operate in both analog and digital signal systems (Japanese Patent Application No. 9-257024) and a TV lens apparatus and a TV lens control unit capable of operating in both systems (Japanese Patent Application No. 10-63025, and Japanese Patent Application No. 10-74019, which corresponds to U.S. patent application Ser. No. 09/275,189 assigned to the assignee of the present application).
The conventional TV lens system having an analog control system (an analog control mode) and a serial communication function (a digital control mode) is normally controlled in the digital control mode, which ensures various functions. If, however, the transmission and reception of data in the serial communication becomes impossible for some reasons, the entire system is suspended completely and cannot be used.
It is therefore an object of the present invention to provide a TV lens system that prevents the complete suspension and can be used continuously even if the operation in the digital control mode becomes impossible.
The above object can be achieved by providing a TV lens system, comprising: a lens drive that drives a TV lens apparatus, the lens drive operating in control modes including an analog control mode and a digital control mode; a communication monitor that monitors communication of the lens drive in the digital control mode; and a switching device that switches the control modes of the lens drive from the digital control mode to the analog control mode if the communication monitor detects the communication being abnormal.
More specifically, the TV lens system of the present invention has the control function for both the analog control mode and the digital control mode. If the system is set in the digital control mode, the signals (or data) are transmitted between the lens control unit and the lens apparatus or the lens drive by way of communication in the digital control mode. The transmission of the data by way of communication controls the lens. The communication monitor monitors the state of the communication in the digital control mode to determine whether the communication is normal or abnormal. If the communication monitor detects the communication being abnormal, the switching device switches the mode to the analog control mode. Thus, the system can be used continuously in the analog control mode even if the communication goes wrong in the digital control mode. The switching device may be operated manually or automatically. A display is preferably provided for informing the user of the abnormality of the communication.